Fluid operated or fluid power cylinders generally include a cylindrical shaped tube or barrel with a cylindrical inner bore in which a piston reciprocally moves in the longitudinal direction. Generally, the barrel of the fluid power cylinder is manufactured of metal, such as aluminum or stainless steel. More commonly, the cylinder barrel is of the conventional round architecture, i.e., a simple torus geometry. A second, more modern type of barrel used in fluid power cylinders includes a square profile made by extrusion of a metal material, such as aluminum. The architecture of the square extension usually includes a variety of complex geometrical patterns, ranging from a simple square or rectangular outer geometry with a round cavity in the middle to a very complex outer geometry with a complex internal geometry.
Fluid power cylinders are controlled by various sensors and switches designed to sense the position of a reciprocating piston within the cylinder. Through these sensors, the mechanisms controlling the action of the fluid power cylinders may determine the position of the piston, or the timing for opening or closing various valves, inlets, or outlets in order to control the fluid pressure working on the piston, and vice versa. Thus, in some applications of fluid power cylinders, and depending on the task to be accomplished, it is often necessary to mount sensors or electrical switches onto the cylinder housing in order to respond to a piston as it travels within the inner bore, or to control operation of the cylinder. The piston often contains some means to activate a sensing device or switch associated with the mounted sensor to help the sensor determine the position of the piston as it travels within the inner bore. Moreover, the fluid power cylinder is often in cooperative coupling with another apparatus or serves as part of a mechanism. The current methods of mounting or clamping sensors or other objects on the fluid power cylinder and the apparatus for achieving such clamping are quite varied.
In many fluid power cylinders, the barrel outer surface is used to clamp position sensors or other devices thereto. One method currently used to hold an object on a cylinder, including a sensor or apparatus, is the tie-rod method. Tie-rods are provided between the end caps and the object is either clamped on the rod or the tie rods are screwed into the object that needs to be held along the cylinder profile. While several variations of the tie-rod types of mounting systems exist in the prior art, most commonly, the cylinder is simply surrounded by tie rods which connect and hold various structures, such as caps or heads, at opposing ends of the cylinder and the tie rods serve as the structure upon which the clamping occurs and the sensors are mounted. The sensor may be held in place via metal or plastic tie-straps. Screw clamp methods are known in the art as well.
In tie-rod mounting systems, the clamp forces used for the placement of the sensors onto the barrel outer surface are rather low. Thus, it is unlikely that clamping of the sensor will distort the cylinder profile or the inner bore wherein the piston travels reciprocally.
However, tie-rod mounting systems present other potential problems. For example, when an object or the cylinder itself needs to be held in place along the barrel surface to avoid movement of the object or avoid movement of the cylinder, the mounting system may slip or pivot on the tie rod. Moreover, in order to properly install or change the clamp mounted with tie rods, one must disconnect the tie rods and remove the cylinder head.
More recent innovations aimed at alleviating the problems with tie rods often do not achieve the desired level of success, or simply trade one problem for another. For example, in U.S. Pat. No. 5,014,950, issued to Ohman et al., a clamping assembly for attaching a magnetically operated electrical switch to a tie rod and against the outside surface of a cylinder is disclosed. The stated goal of the invention is the creation of a clamping device which cooperates with an apparatus to hold that apparatus in a pre-determined position against the outside of a cylinder. Ohman et al. further discloses that the essence of the invention resides in the fact that the cooperating clamp surfaces engage the tie rod and converge toward the cylinder in order to effectively draw the assembly tightly against the outside cylinder surface as the fastening means are tightened. In sum, the '950 patent discloses a clamp construction designed to cause the entire clamp assembly to converge tightly and move against the cylinder wall.
While trying to solve a problem associated with clamping to a tie-rod, the '950 patent creates other potential disadvantages. For example, when clamping on a simple torus profile or square/rectangular extruded type profile, high forces directed towards the center of the profile may affect the housing material in such a way that the inner bore of the cylinder becomes smaller or distorted. As the diameter of the inner bore decreases in size or becomes distorted from its annular shape, the piston running inside the inner bore may bind or become stuck inside the inner bore due to higher friction. The higher friction will in turn cause wear on the piston running surface, which in most cases is a seal or seal with slide bearing combination. This additional wear will adversely affect the life expectancy of the cylinder. Furthermore, when the piston seal wears due to the profile distortion, small openings at the seal can form and the seal will not be able to properly seal. Thus, fluid tightness of the cylinder and piston will be lost. The additional friction will also cause the piston to run slower and the piston travel time to increase.
On the other hand, one may attempt to decrease the forces directed by the clamp on the inner bore by loosening the clamp around the perimeter of the fluid power cylinder; however, this can create other problems. For example, the reciprocal movement of the piston in the inner bore of the cylinder inherently generates high fluid power cylinder forces that may cause the clamped object to come lose. There is also the potential of moving the clamped object out of position due to accidentally hitting the object. This poses a potential hazard to a person standing nearby the object. Moreover, current clamp-on designs are non-smooth designs generally having sharp edges, which pose the threat of potential danger to a person handling such a component. The person may hurt himself or herself by the protruding components of the clamps.
Thus, there remains a need for an improved clamp assembly for securing an apparatus to the cylinder profile of a fluid power cylinder without using a tie rod and without distorting the inner bore of the cylinder or affecting the piston reciprocally traveling therein.